DETERMINATION OF THE AL MOLE FRACTION AND THE BAND-GAP BOWING OF EPITAXIAL ALXGA1-XN FILMS

AlxGa1-xN alloys were grown on c-plane sapphire by plasma-induced mole cular beam epitaxy. The Al content x was varied over the whole composi tion range (0 less than or equal to x less than or equal to 1). The mo lar Al fraction was deduced from x-ray diffraction and for comparison by elastic recoil detection analysis. The composition of the alloys ca lculated from the lattice parameter c underestimates x. This is due to a deformation of the unit cell. The exact Al mole fraction and the bi axial strain of the alloys can be calculated by an additional determin ation of alpha, using asymmetric reflections. The results obtained by x-ray diffraction and elastic recoil detection provide evidence for th e validity of Vegard's law in the AlGaN system. In addition, the devia tion of the band gap from a linear dependence on x was investigated. W e found a downward bowing with a bowing parameter b=1.3 eV. (C) 1997 A merican Institute of Physics.